Personal patches to the xv6 kernel
ab0db651af
The x86-64 doesn't just add two levels to page tables to support 64 bit addresses, but is a different processor. For example, calling conventions, system calls, and segmentation are different from 32-bit x86. Segmentation is basically gone, but gs/fs in combination with MSRs can be used to hold a per-core pointer. In general, x86-64 is more straightforward than 32-bit x86. The port uses code from sv6 and the xv6 "rsc-amd64" branch. A summary of the changes is as follows: - Booting: switch to grub instead of xv6's bootloader (pass -kernel to qemu), because xv6's boot loader doesn't understand 64bit ELF files. And, we don't care anymore about booting. - Makefile: use -m64 instead of -m32 flag for gcc, delete boot loader, xv6.img, bochs, and memfs. For now dont' use -O2, since usertests with -O2 is bigger than MAXFILE! - Update gdb.tmpl to be for i386 or x86-64 - Console/printf: use stdarg.h and treat 64-bit addresses different from ints (32-bit) - Update elfhdr to be 64 bit - entry.S/entryother.S: add code to switch to 64-bit mode: build a simple page table in 32-bit mode before switching to 64-bit mode, share code for entering boot processor and APs, and tweak boot gdt. The boot gdt is the gdt that the kernel proper also uses. (In 64-bit mode, the gdt/segmentation and task state mostly disappear.) - exec.c: fix passing argv (64-bit now instead of 32-bit). - initcode.c: use syscall instead of int. - kernel.ld: load kernel very high, in top terabyte. 64 bits is a lot of address space! - proc.c: initial return is through new syscall path instead of trapret. - proc.h: update struct cpu to have some scratch space since syscall saves less state than int, update struct context to reflect x86-64 calling conventions. - swtch: simplify for x86-64 calling conventions. - syscall: add fetcharg to handle x86-64 calling convetions (6 arguments are passed through registers), and fetchaddr to read a 64-bit value from user space. - sysfile: update to handle pointers from user space (e.g., sys_exec), which are 64 bits. - trap.c: no special trap vector for sys calls, because x86-64 has a different plan for system calls. - trapasm: one plan for syscalls and one plan for traps (interrupt and exceptions). On x86-64, the kernel is responsible for switching user/kernel stacks. To do, xv6 keeps some scratch space in the cpu structure, and uses MSR GS_KERN_BASE to point to the core's cpu structure (using swapgs). - types.h: add uint64, and change pde_t to uint64 - usertests: exit() when fork fails, which helped in tracking down one of the bugs in the switch from 32-bit to 64-bit - vectors: update to make them 64 bits - vm.c: use bootgdt in kernel too, program MSRs for syscalls and core-local state (for swapgs), walk 4 levels in walkpgdir, add DEVSPACETOP, use task segment to set kernel stack for interrupts (but simpler than in 32-bit mode), add an extra argument to freevm (size of user part of address space) to avoid checking all entries till KERNBASE (there are MANY TB before the top 1TB). - x86: update trapframe to have 64-bit entries, which is what the processor pushes on syscalls and traps. simplify lgdt and lidt, using struct desctr, which needs the gcc directives packed and aligned. TODO: - use int32 instead of int? - simplify curproc(). xv6 has per-cpu state again, but this time it must have it. - avoid repetition in walkpgdir - fix validateint() in usertests.c - fix bugs (e.g., observed one a case of entering kernel with invalid gs or proc |
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|---|---|---|
| .cvsignore | ||
| .dir-locals.el | ||
| .gdbinit.tmpl-i386 | ||
| .gdbinit.tmpl-x64 | ||
| .gitignore | ||
| asm.h | ||
| bio.c | ||
| bootmain.c | ||
| buf.h | ||
| BUGS | ||
| cat.c | ||
| console.c | ||
| cuth | ||
| date.h | ||
| defs.h | ||
| dot-bochsrc | ||
| echo.c | ||
| elf.h | ||
| entry.S | ||
| entryother.S | ||
| exec.c | ||
| fcntl.h | ||
| file.c | ||
| file.h | ||
| forktest.c | ||
| fs.c | ||
| fs.h | ||
| gdbutil | ||
| grep.c | ||
| ide.c | ||
| init.c | ||
| initcode.S | ||
| ioapic.c | ||
| kalloc.c | ||
| kbd.c | ||
| kbd.h | ||
| kernel.ld | ||
| kill.c | ||
| lapic.c | ||
| LICENSE | ||
| ln.c | ||
| log.c | ||
| ls.c | ||
| main.c | ||
| Makefile | ||
| memide.c | ||
| memlayout.h | ||
| mkdir.c | ||
| mkfs.c | ||
| mmu.h | ||
| mp.c | ||
| mp.h | ||
| msr.h | ||
| Notes | ||
| param.h | ||
| picirq.c | ||
| pipe.c | ||
| pr.pl | ||
| printf.c | ||
| printpcs | ||
| proc.c | ||
| proc.h | ||
| README | ||
| rm.c | ||
| runoff | ||
| runoff.list | ||
| runoff.spec | ||
| runoff1 | ||
| sh.c | ||
| show1 | ||
| sign.pl | ||
| sleep1.p | ||
| sleeplock.c | ||
| sleeplock.h | ||
| spinlock.c | ||
| spinlock.h | ||
| spinp | ||
| stat.h | ||
| stressfs.c | ||
| string.c | ||
| swtch.S | ||
| syscall.c | ||
| syscall.h | ||
| sysfile.c | ||
| sysproc.c | ||
| toc.ftr | ||
| toc.hdr | ||
| trap.c | ||
| trapasm.S | ||
| traps.h | ||
| TRICKS | ||
| types.h | ||
| uart.c | ||
| ulib.c | ||
| umalloc.c | ||
| user.h | ||
| usertests.c | ||
| usys.S | ||
| vectors.pl | ||
| vm.c | ||
| wc.c | ||
| x86.h | ||
| zombie.c | ||
xv6 is a re-implementation of Dennis Ritchie's and Ken Thompson's Unix
Version 6 (v6). xv6 loosely follows the structure and style of v6,
but is implemented for a modern x86-based multiprocessor using ANSI C.
ACKNOWLEDGMENTS
xv6 is inspired by John Lions's Commentary on UNIX 6th Edition (Peer
to Peer Communications; ISBN: 1-57398-013-7; 1st edition (June 14,
2000)). See also https://pdos.csail.mit.edu/6.828/, which
provides pointers to on-line resources for v6.
xv6 borrows code from the following sources:
JOS (asm.h, elf.h, mmu.h, bootasm.S, ide.c, console.c, and others)
Plan 9 (entryother.S, mp.h, mp.c, lapic.c)
FreeBSD (ioapic.c)
NetBSD (console.c)
The following people have made contributions: Russ Cox (context switching,
locking), Cliff Frey (MP), Xiao Yu (MP), Nickolai Zeldovich, and Austin
Clements.
We are also grateful for the bug reports and patches contributed by Silas
Boyd-Wickizer, Anton Burtsev, Cody Cutler, Mike CAT, Tej Chajed, eyalz800,
Nelson Elhage, Saar Ettinger, Alice Ferrazzi, Nathaniel Filardo, Peter
Froehlich, Yakir Goaron,Shivam Handa, Bryan Henry, Jim Huang, Alexander
Kapshuk, Anders Kaseorg, kehao95, Wolfgang Keller, Eddie Kohler, Austin
Liew, Imbar Marinescu, Yandong Mao, Matan Shabtay, Hitoshi Mitake, Carmi
Merimovich, Mark Morrissey, mtasm, Joel Nider, Greg Price, Ayan Shafqat,
Eldar Sehayek, Yongming Shen, Cam Tenny, tyfkda, Rafael Ubal, Warren
Toomey, Stephen Tu, Pablo Ventura, Xi Wang, Keiichi Watanabe, Nicolas
Wolovick, wxdao, Grant Wu, Jindong Zhang, Icenowy Zheng, and Zou Chang Wei.
The code in the files that constitute xv6 is
Copyright 2006-2018 Frans Kaashoek, Robert Morris, and Russ Cox.
ERROR REPORTS
Please send errors and suggestions to Frans Kaashoek and Robert Morris
(kaashoek,rtm@mit.edu). The main purpose of xv6 is as a teaching
operating system for MIT's 6.828, so we are more interested in
simplifications and clarifications than new features.
BUILDING AND RUNNING XV6
To build xv6 on an x86 ELF machine (like Linux or FreeBSD), run
"make". On non-x86 or non-ELF machines (like OS X, even on x86), you
will need to install a cross-compiler gcc suite capable of producing
x86 ELF binaries (see https://pdos.csail.mit.edu/6.828/).
Then run "make TOOLPREFIX=i386-jos-elf-". Now install the QEMU PC
simulator and run "make qemu".